In Tom's Hardware Guide's June 2013 Grand Prix, Firefox 21 came in third place on the Impact HTML5 game benchmark: http://www.tomshardware.com/reviews/chrome-27-firefox-21-opera-next,3534-7.html http://html5-benchmark.com/

On Windows 7, with HWA ON: browser - score - time taken - lag Firefox 36 - 5031 - 15.71s - 734ms Nightly 37 - 7393 - 12.98s - 214ms Chrome 39 - 7139 - 19.62s - 0ms IE 11 - 7109 - 17.86s - 70ms If somebody could test on Linux or Mac, it would be great. On Windows, Nightly improved a lot recently with the work from the JS GC guys, enough to beat the other browsers. The result also seems to confirm what a web developer told on another bug: Chrome seems to slow down enough to have no lag.

On my MBP running OS X 10.10, Chrome is still beats Firefox: BROWSER SCORE TIME LAG Firefox 34 5516 20.52s 380ms Nightly 37 6205 19.76s 206ms Chrome 39 6751 13.95s 300ms